Method for making optical elements for microlithography, the lens systems obtained by the method and their uses

Abstract

The optical elements for ultraviolet radiation, especially for microlithography, are made from cubic granet, cubic spinel, cubic perovskite and/or cubic M(II)- as well as M(IV)-oxides. The optical elements are made from suitable crystals of Y 3 Al 5 O 12 , Lu 3 Al 5 O 12 , Ca 3 Al 2 Si 3 O 12 , K 2 NaAlF 6 , K 2 NaScF 6 , K 2 LiAlF 6 and/or Na 3 Al 2 Li 3 F 12 , (Mg, Zn)Al 2 O 4 , CaAl 2 O 4 , CaB 2 O 4 and/or LiAl 5 O 8 , BaZrO 3 and/or CaCeO 3 . A front lens used in immersion optics for microlithography at wavelengths under 200 nm is an example of a preferred optical element of the present invention.

1. An optical element in a lens system for microlithography, said optical element comprising cubic spinel, and wherein said cubic spinel consists of (Mg, Zn)Al 2 O 4 , CaAl 2 O 4 , CaB 2 O 4  and/or LiAl 5 O 8 . 
     
     
       2. An optical element in a lens system for microlithography, said optical element comprising cubic perovskite, and wherein said cubic perovskite consists of BaZrO 3  and/or CaCeO 3 . 
     
     
       3. An optical element in a lens system for microlithography, said optical element comprising cubic M(II)-oxides and cubic M(IV)-oxides, and wherein said cubic M(II)-oxides and said cubic M(IV)-oxides are MgO and (Mg, Zn)O. 
     
     
       4. An optical element in a lens system for microlithography, said optical element comprising at least one material selected from the group consisting of cubic garnet, cubic spinel, cubic perovskite, cubic M(II)-oxides and cubic M(IV)-oxides, wherein said at least one material is crystalline and has a stress birefringence of less than 1 nm/cm at a wavelength of 193 nm, a uniformity of refractive index Δn of less than 1 ppm and a spectral absorption coefficient, K ini , at 193 nm of less than or equal to 2×10 −3  cm −1 . 
     
     
       5. A method of making an optical element for ultraviolet radiation, said method comprising the steps of:
 a) growing at least one single crystal of at least one material from a melt, said at least one material being selected from the group consisting of cubic garnet, cubic spinel, cubic perovskite, cubic M(II)-oxides and cubic M(IV)-oxides; and 
 b) forming said optical element from said at least one single crystal; 
 wherein said at least one single crystal is grown from the melt by a Bridgman-Stockbarger process, a Vertical-Gradient-Freeze process, a Czochralski Process, or a Nacken-Kyropoulos process. 
 
     
     
       6. A method of making an optical element for ultraviolet radiation, said method comprising the steps of:
 a) providing a powder of nanoparticles, said nanoparticles comprising at least one material, said at least one material being selected from the group consisting of cubic garnet, cubic spinel, cubic perovskite and cubic M(II)-oxides; 
 b) sintering said powder of nanoparticles to form an opto-ceramic material; and 
 c) forming the optical element from said opto-ceramic material. 
 
     
     
       7. An optical element in a lens system for microlithography, said optical element comprising at least one material selected from the group consisting of cubic perovskite, Lu 3 Al 5 O 12 , (Mg, Zn)Al 2 O 4 , MgO and (Mg, Zn)O;
 wherein said at least one material is crystalline and has a stress birefringence of less than 1 nm/cm at a wavelength of 193 nm, a uniformity of refractive index Δn of less than 1 ppm and a spectral absorption coefficient, K ini , at 193 nm of less than or equal to 2×10 −3  cm −1 . 
 
     
     
       8. A method of making an optical element for ultraviolet radiation, said method comprising the steps of:
 a) growing at least one single crystal of at least one material from a melt, said at least one material being selected from the group consisting of cubic perovskite, Lu 3 Al 5 O 12 , (Mg, Zn)Al 2 O 4 , MgO and (Mg, Zn)O; and 
 b) forming said optical element from said at least one single crystal, 
 wherein the at least one single crystal is grown from the melt by a Bridgman-Stockbarger process, a Vertical-Gradient-Freeze process, a Czochralski Process, or a Nacken-Kyropoulos process. 
 
     
     
       9. A method of making an optical element for ultraviolet radiation, said method comprising the steps of:
 a) providing a powder of nanoparticles, said nanoparticles comprising cubic perovskite, Lu 3 Al 5 O 12 , (Mg, Zn)Al 2 O 4 , MgO and (Mg, Zn)O; 
 b) sintering said powder of nanoparticles to form an opto-ceramic material having a crystallite size in a range of from about 10 to 100 μm; and 
 c) forming the optical element from said opto-ceramic material. 
 
     
     
       10. An optical element in a lens system for microlithography, said optical element comprising at least one cubic garnet,
 wherein said at least one cubic garnet consists of K 2 NaAlF 6 , K 2 NaScF 6 , K 2 LiAlF 6  and/or Na 3 Al 2 Li 3 F 12 .